I received a response outside this forum from an owner with the same problem. The owner identified the location of the freshwater tank outward of the lower fuel tank and was able to access the area only by drilling through two layers of plywood under the floor galley storage area. However, to solve the tank monitor problem, they installed at Jakmeter (
http://www.jakmeter.com/) next to their water pump. Although they have to reset the meter each time they fill their water tanks, they now have an accurate measure of what is in their tanks. I will be implementing the same solution.
-Mark